1. Field of the Invention
This invention relates to decontamination methods and apparatus, and in particular to methods of and apparatus for using photosensitizers and light to treat chemical and/or biological contaminants on surfaces and in aerosol clouds.
2. Related Art
Biological decontamination is the destruction of microorganisms, and pathogens, such as bacteria, both vegetative and sporulative, bacterial spores, viruses, mycoplasma, protozoans, oocysts, and toxins. Chemical contamination is the destruction of chemical contaminants, pesticides, chemical warfare agents, and other toxic substances. Current methods of decontamination and disinfection of surfaces include chemical washing, fumigation, heat treatment, and irradiation. Chemical washing includes washing the surface with anything from simple soap and water, to sodium hypochlorite (bleach), DS-2, hydrogen peroxide, alkali, hexachlorophene, and quaternary amines. Fumigation includes exposing an object or surface of an object to a fumigant. A common fumigant is ethylene oxide (EtO), a flammable, carcinogenic/mutagenic compound; another is ozone, a toxic gas. Heat treatment includes wet and dry autoclaving, including steam heating, and high temperature heating in an oven. Heat treatment is sometimes augmented with substances that reduce the heat resistance of bacterial spores, such as ethylene oxide, hydrogen peroxide, garlic oil, nisin, subtilin methyl ester, and others. For example, it is known in the art that microwave heating combined with application of hydrogen peroxide is an efficacious bactericidal treatment. Irradiation, such as with ionizing radiation is also used to alter chemical contamination and/or to disinfect. Ionizing radiation is most commonly performed by exposure to gamma rays from a radioactive source, or by exposure to x-rays or electrons from an electron accelerator.
Each of these methods has proven to be effective for certain situations, but each has certain problems. Chemical washing in the field is environmentally unsound because it results in distribution of toxic chemical washes. The use of fumigants, including ethylene oxide, has associated occupational and operational hazards. Heat treatment in autoclaves is not practical for large objects and cannot be used for decontaminating people, or for equipment that would be harmed by heat. Irradiation requires either a radioactive source or an accelerator, which are generally cumbersome and require either substantial shielding or ‘standoff’ distance for safety for people and animals. Thus, for reasons of cost, portability, environmental impact, or safety, the existing methods have limited practicality and attractiveness.
Surface cleaning with UV light has been used in the preparation of microelectronic materials and devices, but has limited effect on destroying chemical contamination. Reactive gas can be used in combination with UV light, but this process must be performed in a controlled environment, either a high average power laser UV source or high flow gas jet must be used to achieve satisfactory cleaning rates.
UV light is also used in disinfection processes, but typically requires enormous fluence and exposure (absorbed energy per unit area). See, for example, Clark et al., U.S. Pat. Nos. 5,786,598 and 5,925,885, Dunn, U.S. Pat. No. 4,871,559, Hiramoto, U.S. Pat. No. 4,464,336, and Busnell, U.S. Pat. No. 5,768,853, incorporated herein by reference. This requires multiple UV light sources and long exposure times which are not practical for many applications such as decontamination or disinfection of people, equipment, spaces that must be returned to activity or use as quickly as possible. Although the use of more powerful light sources can reduce exposure times, high exposure to UV light can cause degradation of many materials and, in the case of people, harmful biological effects such as erythema and burn. UV light reflected off some surfaces may pose a hazard to people and property nearby.
Finally, higher average power and higher fluence sources generally have lower efficiencies, increasing power consumption and generating excess heat.
UV light has also been used in conjunction with catalysts for decontaminating water and stack gases, and used in connection with ozone and chlorination process, but these methods are not applicable to surface decontamination. See, for example, Dunn, U.S. Pat. Nos. 5,658,530 and 5,900,211, incorporated herein by reference.
Hydrogen peroxide compositions have been used as disinfectants. See Bowing et al., U.S. Pat. Nos. 4,051,058 and 4,051,059, incorporated herein by reference. UV light and hydrogen peroxide have been used in the sterilization of cartons. See Bayliss and Waites, “The Combined Effect of Hydrogen Peroxide and Ultraviolet Irradiation on Bacterial Spores” 47 Journal of Applied Bacteriology 263-269 (1979), and Bayliss and Waites “The Effect of Hydrogen Peroxide and Ultraviolet Irradiation on Non-sporing Bacteria” 48 Journal of Applied Bacteriology 417-422 (1980), Bayliss and Waites, “Resistance of Serratia marcescens to Hydrogen Peroxide” 50 Journal of Applied Bacteriology 131-137 (1981), and Bayliss and Waites, “Resistance of Structure of Spores of Bacillus subtilis” 50 Journal of Applied Bacteriology 379-390 (1981), incorporated herein by reference. In one method hydrogen peroxide vapor or mist is applied within an enclosed volume and subsequent exposure to UV light. In another method a solution of hydrogen peroxide having a concentration that is less than 10%, is applied and UV light with wavelength less than 325 nm, is applied. Hydrogen peroxide and UV light is also used in the treatment of wastewater.
All of these previously applied methods and the apparatus associated with these methods are not well suited for decontamination or disinfection in a relatively unconfined or uncontrolled environment or situation. Examples of such situations include the decontamination/disinfection of surfaces of people, their garments, equipment, and occupiable spaces as part of the consequence management of a natural disaster, an industrial accident, a transportation accident, criminal violence, terrorist attack, or in a military situation, e.g., chemical or biological warfare. Another example of a relatively uncontrolled environment is a drifting cloud of hazardous chemical agent or infectious biological agent. Such a cloud might occur as a result of the any of the above situations.
There are many additional situations in which a method and apparatus that can be rapidly deployed or used on an occasional basis in variable environmental conditions, would be beneficial. Applications for such a system include cleaning and disinfection of surfaces in medical, food preparation, and pharmaceutical facilities and the decontamination and disinfection of personnel and equipment following exposure to military chemical and biological warfare agents as part of the demilitarization of such materials. Other applications include the disinfection of medical implements, medical waste containers, and medical waste treatment equipment. There are many additional situations in which benefits would be realized by a method and apparatus that can be rapidly deployed or used on an occasional basis or with variable environmental conditions.